1. Field of the Invention
The present invention generally relates to magnetic storage of information, and particularly to a spin-valve magnetoresistive sensor and a magnetic head having such a spin-valve magnetoresistive sensor.
2. Description of the Related Art
Presently, anisotropic magnetoresistive (AMR) sensors are used extensively for a magnetic head of a hard disk drive (HDD) apparatus. Due to the tendency of increasing recording density of magnetic recording apparatuses, there is a growing need for a magnetic head having a spin-valve magnetoresistive sensor, which provides a sensitivity superior to an AMR sensor.
FIG. 1 is a partially cut-away perspective diagram of a composite magnetic head 130 including the spin-valve magnetoresistive head 100 of the related art. The composite magnetic head 130 incorporates the spin-valve magnetoresistive head 100 as a reading (reproducing) head of the hard disk drive apparatus and also incorporates a writing (recording) head. FIG. 1 also shows a hard disk 27 as a recording medium. In the figure, the hard disk 27 is arranged so as to oppose the composite magnetic head 130. The basic structure of the composite magnetic head 130 is substantially the same as the structure of the composite magnetic head 30 of the present invention. Therefore, further detailed description is omitted here. The structure of the composite magnetic head 130 of the related art can be understood when reading the detailed description of FIG. 8 by replacing the spin-valve magnetoresistive head 10 with the spin-valve magnetoresistive head 100 of the related art.
FIG. 2 is a partially cut-away perspective view showing a spin-valve magnetoresistive head 100 using a spin-valve magnetoresistive sensor of the related art. Further, FIG. 3 is a side view showing the spin-valve magnetoresistive head 100 of FIG. 2. In the following, the spin-valve magnetoresistive head 100 will be described in detail with reference to FIGS. 2 and 3.
The spin-valve magnetoresistive head 100 includes a lowermost underlayer 111 of tantalum (Ta) and an uppermost capping layer 116 also of Ta, and a spin-valve magnetoresistive sensor is interposed between the underlayer 111 and the capping layer 116. The spin-valve magnetoresistive sensor (or film) includes a free layer 112 of a ferromagnetic material, a non-magnetic layer 113 of a non-magnetic conductive material such as copper (Cu), a pinned magnetic layer 114 of a ferromagnetic material such as a cobalt-iron-boron (CoFeB) alloy, and a pinning layer 115 of an anti-ferromagnetic material, which may be formed of an ordered alloy made of palladium-platinum-manganese (PdPtMn), in the state that the layers 112-115 are stacked consecutively on the underlayer 111. The free layer 112 typically includes a first ferromagnetic layer 112a of nickel-iron (NiFe) provided on the underlayer 111 and a second ferromagnetic layer 112b of a cobalt-iron-boron (CoFeB) alloy provided on the first ferromagnetic layer 112a. 
In this context, the ordered alloy used for the pinning layer 115 is understood as an anti-ferromagnetic alloy which does not exhibit magnetism when initially formed as the anti-ferromagnetic layer 115. On the other hand, the ordered alloy exhibits a stable magnetization when its magnetization is aligned as a result of magnetizing process conducted under a suitable condition.
The above-described spin-valve magnetoresistive head is manufactured first by providing the underlayer and then providing other layers described above in the order shown in FIGS. 2 and 3. Then, all the layers including the spin-valve magnetoresistive sensor are patterned to form a rectangular body, and electrode terminals 117a, 117b of a metal such as gold (Au) are provided on the uppermost capping layer 116 with a mutual separation from each other.
In the spin-valve magnetoresistive head 100 of FIG. 3, the area between the electrodes 117a and 117b and designated as S serves as the signal sensing area of the spin-valve magnetoresistive sensor. In the following text, X-, Y-, and Z-directions are defined as follows in order to make a clear explanation of, for example, the magnetizing direction of the spin-valve magnetoresistive sensor of the spin-valve magnetoresistive head 100. Thus, the Z-direction is defined as a direction of the thickness of the spin-valve magnetoresistive sensor. The Y-direction is a direction perpendicular to the Z-direction. It should be noted that the foregoing electrodes 117a and 117b are provided at the respective opposite ends of the rectangular body forming the spin-valve magnetoresistive sensor in the cross-sectional view taken in the Y-direction. The X-direction (the height) is a direction perpendicular to the Y-Z plane.
In the following text, it is assumed that the magnetization of the free layer 112 points in the Y-direction in the state where there is no external magnetic field applied to the free layer 112. In other words, the free layer 112 has an easy axis of magnetization pointing in the Y-direction. Also, a term xe2x80x9corientationxe2x80x9d is understood to mean a predetermined direction, which may be shown by an arrow in the figures. A term xe2x80x9cdirectionxe2x80x9d can imply both opposite orientations having positive and negative signs.
During the operation of the spin-valve magnetoresistive head 100 of the related art, a sense current Is is caused to flow through the signal sensing region S between the two electrode terminals 117a, 117b, and the spin-valve magnetoresistive head 100 is caused to scan over a magnetic recording medium (not shown) such as a magnetic disk. Then, the electric resistance of the spin-valve magnetoresistive sensor changes in response to a signal magnetic field Hsig originating from the magnetic recording medium in the X-direction. Thus, the signal magnetic field of the magnetic recording medium can be detected as a change of the voltage appearing across the electrodes 117a and 117b. 
With such a spin-valve magnetoresistive head 100, it is preferable that the resistance of the spin-valve magnetoresistive sensor changes linearly with respect to direction of the signal magnetic field Hsig such that the resistance increases when the signal magnetic field Hsig has a first orientation and such that the resistance decreases when the signal magnetic field Hsig has a second, opposite orientation It should be noted that the resistance of the spin-valve magnetoresistive sensor becomes minimum when the magnetization Mf of the free layer 112 and the magnetization Mp of the pinned magnetic layer 114 are parallel and becomes maximum when the magnetization Mf of the layer 112 and the magnetization Mp of the layer 114 are anti-parallel. In order to achieve this, the direction of magnetization Mp of the pinned magnetic layer 114 is pinned in the X-direction by establishing an exchange coupling between the pinned magnetic layer 114 and the anti-ferromagnetic layer 115. Then, when the signal magnetic field Hsig is zero, the direction of magnetization Mf of the free layer 112 points in the Y-direction as stated above.
Now, due to the increase in the recording density of the information recorded on a recording medium such as a hard disk, there is a tendency that the size of the individual magnetic spots formed on the magnetic disk becomes smaller and smaller, and because of this, the signal magnetic field Hsig which the spin-valve magnetoresistive head 100 is supposed to pick up tends to become very weak. In order to compensate for the weakening of the signal magnetic field Hsig, it is necessary to increase the magnetic resistance ratio (MR-ratio) xcex94 xcfx81/xcfx81 to obtain a larger signal or S/N ratio. In order to achieve this, either the thickness (Z-direction) or the height of the sensor (X-direction) of the spin-valve magnetoresistive sensor has to be reduced.
Firstly, a process of reducing the thickness (Z-direction) is considered. The layer having the greatest thickness in the spin-valve magnetoresistive sensor is the anti-ferromagnetic layer 115, which generally requires a thickness of more than 200 xc3x85. If the thickness of the anti-ferromagnetic layer 115 is less than 100 xc3x85, the exchange coupling magnetic field for fixing the orientation of magnetization Mp of the pinned magnetic layer 114 works little. Thus, there is a risk that the direction of magnetization Mp may be reversed easily by a disturbance such as an externally applied heat. Further, in view of maintaining the magnetic proper necessary for the spin-valve magnetoresistive sensor, each of the pinned magnetic layer 114 and the free layer 112 has to have a sufficient thickness. Therefore, there is a limitation in reducing the thickness of the pinned magnetic layer 114 or the thickness of the free layer. 112.
Secondly, a process of reducing the height of the sensor (X-direction) is considered.
Technically, it is possible to reduce the height of the layers. However, when the height of the sensor becomes too small, the distance between the side edges of the pinned magnetic layer 114 extending in the Y-direction becomes so small that the effect of so-called counteracting magnetic field becomes predominant. Then, the magnetic state of the pinned magnetic layer 114 becomes unstable and there arises a problem that the detection of the magnetic field becomes unstable.
Recently, in order to solve the problem related to counteracting-magnetic field, a spin-valve magnetoresistive sensor is proposed in which the pinned magnetic layer includes a first pinned magnetic layer, a second pinned magnetic layer, and an intermediate layer provided between the first and second pinned magnetic layers. However, with such a structure, a disordered metal of, for example, NiO is used as an anti-ferromagnetic layer. Therefore, the anti-ferromagnetic layer already exhibits a magnetic property at an instant when the pinned magnetic layer is stacked thereon. Accordingly, there are many problems in manufacturing a spin-valve magnetoresistive sensor while maintaining the above-described preferable relationship between the pinned magnetic layer and the free layer.
As has been described above, there are many problems related to development of the spin-valve magnetoresistive sensor. The present invention is related to a method in which the height of the sensor (X-direction) is reduced. More specifically, the present invention relates to a structure including a pinned magnetic layer having a first pinned magnetic layer, a second pinned magnetic layer, and an intermediate layer provided between the first and second pinned magnetic layers. Also, an alloy used for the anti-ferromagnetic layer in the present invention does not exhibit a magnetic property when initially produced as an anti-ferromagnetic layer, but will exhibit the magnetic property when its structure is aligned according to a magnetizing process under a certain condition.
The ordered alloy used for the anti-ferromagnetic layer does not exhibit a magnetic property directly after production of the spin-valve magnetoresistive sensor. The alloy is anti-ferromagnetized (aligned) after implementing a heat treatment in a magnetic field. Thus, the magnetization of the pinned magnetic layer can be fixed. The ordered alloy exhibits such a property due to the fact that the metal crystals will be aligned in a predetermined direction and thus undergoes a phase change from a face-centered cubic structure (fcc) to a face-centered tetragonal structure (fct).
With the spin-valve magnetoresistive sensor of the related art, since the magnetization of the pinned magnetic layer is fixed after the layers have been produced, the heat treatment is implemented while applying a magnetic field of over 2500 Oe (Oersted) in the X-direction. Then, in order to strengthen a magnetic anisotropic property of the free layer, a heat treatment is implemented while applying a predetermined magnetic field in the Y-direction.
However, when a magnetization process similar to that of the related art is implemented on a structure having pinned magnetic layer including a first pinned magnetic layer, a second pinned magnetic layer, and an intermediate layer provided between the first and second pinned magnetic layers, there arises a problem that the orientation of magnetization of the pinned magnetic layer deflects from the X-direction and inclines in the Y-direction. The orientation of magnetization of the pinned magnetic layer and the orientation of magnetization of the free magnetization layer are ideally mutually perpendicular, but an inclination of xc2x120 degrees from a right angle is allowable. However, with an inclination exceeding xc2x120 degrees, a linear output response cannot be achieved with respect to the input of an external signal magnetic field Hsig. Accordingly, there is a problem that a reproduction waveform of the output voltage is deformed.
Accordingly, it is a general object of the present invention to provide a spin-valve magnetoresistive sensor which can solve the above-described problems.
It is another and more specific object of the present invention to provide a spin-valve magnetoresistive sensor which can control the problems related to antimagnetic field and can solve the problems of the related art.
In order to achieve the above objects according to the present invention, a spin-valve magnetoresistive sensor includes:
a free layer of a ferromagnetic material;
a non-magnetic layer provided on the free layer;
a pinned layer provided on the non-magnetic layer; and
a pinning layer of an anti-ferromagnetic material provided on the pinned layer, the anti-ferromagnetic material being an ordered alloy containing manganese.
The pinned layer includes:
a first pinned layer of a ferromagnetic material;
a second pinned layer of a ferromagnetic material provided on the first pinned layer; and
an intermediate layer interposed between the first and second pinned layers such that the first and second pinned layers establish a super-exchange interaction in an anti-parallel manner.
The second pinned layer has a magnetic moment smaller than a magnetic moment of the first pinned layer.
With the spin-valve magnetoresistive sensor described above, by using an ordered alloy including manganese as an anti-ferromagnetic layer, a preferable relationship between the above-described pinned magnetic layer and the free layer can be easily achieved. Accordingly, with a multilayered pinned magnetic layer, the spin-valve magnetoresistive sensor can be further miniaturized and thus can achieve a thin-film structure of reduced thickness.
It is still another object of the present invention to provide a method of manufacturing a spin-valve magnetoresistive sensor of the above-described type.
In order to achieve the above object, a method of manufacturing a spin-valve magnetoresistive sensor includes the steps of:
a) forming a multilayered body in an order of the free layer, the non-magnetic layer, the first pinned layer, the intermediate layer, the second pinned layer, and the anti-ferromagnetic layer;
b) implementing a first heat treatment within a magnetic field for regulating a magnetic state of the pinning layer and for fixing an orientation of magnetization of the first and second pinned layers; and
c) implementing a second heat treatment within a magnetic field for regulating a magnetic anisotropic property of the free layer in an environment with a lower temperature and a weaker magnetic field than in the first heat treatment within the magnetic field.
It is yet another object of the present invention to provide a spin-valve magnetoresistive sensor in which a heat treatment in a magnetic field, which is similar to that of the double-layered pinned layer, can be applied to a single-layered pinned layer of the related art.
In order to achieve the above object, a magnetic head having a spin-valve magnetoresistive sensor includes:
a free layer provided on the non-magnetic layer,
a non-magnetic layer provided on the free layer;
a pinned layer provided on the non-magnetic layer; and
a pinning layer of an anti-ferromagnetic material provided on the pinned layer, the anti-ferromagnetic material being an ordered alloy containing manganese;
The direction of magnetization of the pinned magnetic layer and an easy axis of magnetization of the free layer are at a right angle or within xc2x120 degrees of the right angle. The pinned layer has an effective anisotropic magnetic field Hua of a magnitude of greater than or equal to about 600 Oe.
With the structure described above, the orientation Mf of the magnetization of the free layer rotates with respect to a signal magnetic field Hsig from an external magnetic recording medium. Thus, the resistance of the spin-valve magnetoresistive sensor can be changed linearly.
The present invention further relates to a magnetic head having the spin-valve magnetoresistive sensor described above and a magnetic recording medium drive apparatus having a magnetic head provided with a spin-valve magnetoresistive sensor.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.